Expanded PasswordHash

Fixes #52.
- Added Moderate to HashSalsa208Sha256Limit
- Renamed HashSalsa208Sha256 (crypto_pwhash_scryptsalsa208sha256_str) to
HashSalsa208Sha256String
- Renamed HashSalsa208Sha256Verify to HashSalsa208Sha256StringVerify
- Added HashSalsa208Sha256 (crypto_pwhash_scryptsalsa208sha256) and also
some more tests.

HashSalsa208Sha256InteractiveTest() fails on my current computer
(notebook).  The libsodium doc says: if the computation didn't complete,
usually because the operating system refused to allocate the amount of
requested memory.
So i changed the Exception type of the Methods to: OutOfMemoryException.